Despite its efficacy, bupropion's mechanism of action is unclear. Attenuation of abstinence-associated increase in craving and withdrawal symptoms has been suggested as possible mechanisms of bupropion's effect on smoking behaviour in a few randomized clinical trials (Jorneby et al., 1999; Shiffman et al., 2000; Lerman et al., 2002; Durcan et al, 2002). However, these effects are not universally demonstrated (Hurt et al., 1997; Shiffman et al., 2000). Other possible bio-behavioral mechanisms have remained largely unexplored. Using positron emission tomography (PET) it has been shown that in contrast to untreated smokers, when bupropion-treated smokers were exposed to cigarette-related cues there was less metabolic activation in their anterior cingulate cortex, a region of the brain previously shown to be activated by cigarette cues (Brody et al., 2004;Brody et al., 2002).